Modifications to reduce bycatch in prawn trawls: A review and framework for development

The incidental capture of non-target species fromprawn trawling has recently attracted worldwide attention. Primarily, concerns arisefrom the perception that prawn trawls catch anddiscard large numbers of juveniles of species that,when larger, are targeted in other commercial andrecreational fisheries. While several managementoptions are available, the majority of fisheries inthe world have attempted to address this issue throughphysical modifications to trawls, designed to improveselectivity. The types of modifications used reflectfishery-specific characteristics; however, mostcan be broadly classified into twocategories, including: (1) those that separate speciesby differences in behaviour; and (2) those thatmechanically exclude unwanted organisms according totheir size. In the present paper, I provide achronological review of publications in the primaryliterature that describe experiments examiningmodifications within these categories. This reviewshows that inherent variabilities among differentfisheries greatly influence the types of designs thatneed to be applied and although some designs have thepotential for application across different fisheries,significant modification and re-evaluation are oftenrequired. By collating information from previousstudies, I also propose a framework encompassingthe various stages involved in developing and applyingsuccessful modifications in prawn-trawl fisheries. The key stages identified include: (1) quantificationof bycatches and accumulation of fishery-relatedinformation; (2) examination and re-evaluation ofmodifications; (3) assessment of damage inflicted onescaping individuals; and (4) promotion of recommendeddesigns.